Just a further update on this now that it has been discussed at our end. This isn't trivial in our case because of the way our system is configured, but it isn't impossible either. We have assigned this an issue number in our system, and someone will look in to it when time allows.

Actually, I'm in the process of setting it up on my inhouse dovecot server. Since my dovecot set up is plain vanilla, it's just a question of finding the time to add the plugins and rules to the configuration (and not horking a working server as an unintended consequence while I'm at it).